The present invention relates to a bio-inorganic hybrid composite which is able to retain and carry bio-materials with stability and reversible dissociativity. Also, the present invention is concerned with a method for preparing such a bio-inorganic hybrid composite.
Generally, most inorganic compounds having lamellar structures, such as aluminosilicate, metal phosphate, etc, have a feature of being able to retain various materials in their interstices. In this regard, a variety of functional guest chemical species can be introduced into the interstices by subjecting the metal ions composing lattice layers to isomorphorous substitution to generate layer charges or modifying the lamellar in such a way that it is provided with physical and chemical absorptivity. Also, it is well known that the pore sizes of porous inorganic compounds, such as crosslink clay, MCM-41, etc, are controlled to physically adsorb selective sizes of molecules. Layered double hydroxides (hereinafter referred to as "LDH"), which are kinds of the inorganic compounds having lamellar structures, are called anionic clays, consisting of positively charged metal hydroxide layers between which anions counterbalancing the positive charges and water are intercalated.
As a rule, these composites are represented by the following chemical Formula: EQU [M.sup.2+.sub.1-x N.sup.3+.sub.x (OH).sub.2 ][A.sup.n- ].sub.x/n.yH.sub.2 O
wherein,
M is a bivalent metal cation, selected from alkaline earth metals or transition metals, such as Mg.sup.2+, Ni.sup.2+, Cu.sup.2+, Zn.sup.2+ and the like, PA1 N is a trivalent metal cation, selected from transition metals, such as Al.sup.3+, Cr.sup.3+, Fe.sup.3+, V.sup.3+, Ga.sup.3+ and the like, PA1 A is an anionic chemical species with n charges, such as NO.sub.3.sup.-, CO.sub.3.sup.2-, Cl.sup.-, SO.sub.4.sup.2-, metalate, anions of organic acids, etc, PA1 x is a rational number between 0 to 1; and PA1 y is a positive number.
The layer charge densities of the composites can be controlled by changing the metal ratios according to x. Various anions, denoted by A in the LDH, can be easily introduced between the metal hydroxide layers through ion exchange reaction and coprecipitation.
LDH and their derivatives, which are of technical importance in catalytic reactions, are put into spotlight as lamellar nano-composites useful in various fields, including separation technology, optics, medical science, and engineering, and active research has been directed to the composites of interest. For example, hydrotalcite, a mineral name for the compounds based on magnesium and aluminum with similar structures to those of LDH, represented by [Mg.sub.3 Al(OH).sub.8 ].sup.+ [0.5CO.sub.3.multidot.mH.sub.2 O].sup.-, was investigated for the structure of intercalated carbonate anions and water by use of .sup.1 H and .sup.13 C-NMR ["Ordering of intercalated water and carbonate anions in hydrotalcite-An NMR study" Journal Physical Chemistry, 1994, 98, 4050-4054]. A synthesis method for crosslinking precursors of the Mg.sub.3 Al LDH intercalated with hydroxides and adipate through ion exchange reaction with the aid of polyoxometalate (P.sub.2 W.sub.18 O.sub.62.sup.6- or Co.sub.4 (H.sub.2 O).sub.2 (PW.sub.9 O.sub.34).sub.2.sup.10-) and assay results for the structural and thermal properties of the resulting composites are reported in ["Layered double hydroxides intercalated by polyoxometalate anions with keggin (.alpha.-H.sub.2 W.sub.12 O.sub.40.sup.6-), dawson (.alpha.-P.sub.2 W.sub.18 O.sub.62.sup.6-), and finke (Co.sub.4 (H.sub.2 O).sub.2 (PW.sub.9 O.sub.34).sub.2.sup.10-) structures", Inorganic Chemistry, 1996, 35, 6853-6860]. Structural properties of some LDH are introduced, along with kinds and structures of possible metal cations and common intercalated anions in ["Crystal structures of some double hydroxide minerals", Mineralogical Magazine, 1973, 39[304], 377-389]. A survey of LDH and their derivatives, including their historical backgrounds, possible-components (e.g., kinds of metal cations and intercalated anions), structural properties, and applicability is also found in ["Hydrotalcite-type anionic clays: Preparation, Properties and Applications", catalysis Today, 1991, 11, 173-301].
Being useful as gene carriers, bacteria or cationic liposomes have a feasible possibility of causing side effects owing to their own toxicity and a problem of eliciting immune responses and showing poor expression rates.
Therefore, there remains a need for a structure for retaining and carrying bio materials.